(1) Field of the Invention
This invention relates generally to injection molding machines, and more particularly to material feed systems for injection molding machine injection units.
(2) Prior Art
Heretofore with injection molding of glass reinforced polyester, the material has been hand-laid into the feed hoppers of injection molding machine injection units. The particular material involved is stiff and several centimeters or more thick, and have fibers several thicknesses long, which are characteristics that are desirable in the end product properties. If the material is "worked" too much prior to the injection molding operation, the material may be degraded and lose these valuable properties. To minimize the degradation, the material should not be handled nor "worked" excessively which would otherwise break and thus shorten the fibers in the material reducing its strength.
U.S. Pat. No. 3,979,488 to Greenhalgh et al shows a feed mechanism for an injection molding machine. This feed mechanism comprises several reciprocable screws each in long cylindrical material flow paths which would be detrimental to the final properties of any thickened material of the type utilizable in the present invention.
U.S. Pat. No. 4,003,498 to Monegham discloses an apparatus for feeding high bulk material to an extrusion apparatus, however, the system includes an agitated hopper, a flexible auger in a very long closed path leading to a plasticating screw. Such a feed system would destroy the fiber structure of glass reinforced polyesters which are the compounds "worked" in the present invention.
Another machine know in the prior art is a Farrel auger-hopper wherein a first plunger and second plunger are arranged on either side of an extruder screw. The plungers act to feed hot melt thermoplastic material into the extruder screw for processing into pellet form. Such a system used to feed glass reinforced polyester material has been partially tested by Farrel, but has not been applied under production conditions.
It is thus an object of the present invention to provide a material feed system for feeding long fibered glass reinforced polyester material into an injection molding machine injection unit with minimal working or breaking down of the glass fibers prior to their being injection molded.
It is a further object of the present invention to provide a flow path for glass reinforced polyester material entering the injection unit which is as linear as practicable and comports well with the direction of extrudite from the injection unit.